1. Field of the Invention
The present invention relates to a mechanism for tilting a microscope used for an appearance inspection device capable of inspecting wafers in a process such as during the production of semiconductor devices, after the formation of thin films, after etching or after washing.
2. Description of the Related Art
Objects of which the appearance is to be inspected in the IC process chiefly include photomasks, wafers and reticules. In inspecting pattern defects on the wafers, a microscope is generally and widely used for inspecting irregular line widths, scars, missing portions on the patterns that cannot be discovered by the inspection of electric properties, and for sampling inspection during the production steps.
A wafer is usually inspected by using a microscope in a manner as shown in FIG. 12. That is, a wafer 3 to be inspected is secured, by vacuum gripping or a similar method, onto a wafer chuck 2 provided on a moving stage 1 that is allowed to move in the x-direction, Y-direction and Z-direction and to rotate in .theta.-direction. Over the wafer, a microscope 7 is placed via a tilting sub-base, a tilting base 5 and a plate 6. The microscope is provided with plural kinds of objectives 8, and a predetermined objective is brought to an inspection position on the wafer that is to be inspected by revolving an electrically-driven revolver 9.
To vividly and correctly catch the image on the wafer, the optical axis of the objective must be at right angles with the surface of the wafer. Therefore, a tilting mechanism is provided for adjustment. There has heretofore been employed a tilting mechanism shown in FIGS. 13 and 14. In order to support the tilting base 5 and the tilting sub-base 4 while maintaining a gap, the tilting mechanism is provided with gap-adjusting means comprising a pair of a fastening bolt 10 and a set screw 11 at four corners. The tilting base 5 has through holes larger than the outer diameter of the bolt for passing the fastening bolt 10 therethrough but smaller than the head of the fastening bolt, and further has threaded holes for the set screws 11 neighboring the through holes. The tilting sub-base 4 has threaded holes for receiving the fastening bolts 10, and the set screws 11 are set onto the tilting sub-base 4.
To expand the gap between the tilting base 5 and the tilting sub-base 4 in this tilting mechanism, the fastening bolt 10 is turned and is lifted up to create a gap between the lower surface of the head of the fastening bolt and the upper surface of the tilting base. In this state, the set screw 11 is turned to raise the tilting base 5 so that it comes in contact with the lower surface of the head of the fastening bolt. To narrow the gap, the set screw 11 is turned in the reverse direction to lower the tilting base 5 and, then, the fastening bolt is also turned reverse so as to be screwed therein.
Relying on the operations of both the fastening bolt 10 and the set screw 11 as described above, the gap is adjusted at one corner between the tilting base 5 and the tilting sub-base 4. Since the supports exist at four points, this operation for adjustment must be executed at all of four points at four corners, which is very cumbersome. This difficulty in the adjustment makes it impossible to accomplish fine adjustment. Also, a change takes place with the passage of time since there remains a large residual stress after the fastening by using the fastening bolts and set screws.